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| | </syntaxhighlight> | | </syntaxhighlight> |
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| − | === Python Example 1 === | + | === Beginner tutorials === |
| − | * Receive laser scan from robot to decide if free
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| | | | |
| − | <syntaxhighlight lang="python" line='line'>
| + | * Exercise 1 - [https://wiki.cogni.io/index.php/HamsterPythonExample1 | Process laser Scan ] |
| − | #!/usr/bin/env python
| + | * Exercise 2 - [https://wiki.cogni.io/index.php/HamsterPythonExample2 | Process inertial measurement unit (IMU) ] |
| − | import rospy
| + | * Exercise 3 - [https://wiki.cogni.io/index.php/HamsterPythonExample3 | Move until collision ] |
| − | from sensor_msgs.msg import Imu
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| − | | |
| − | def is_free(ranges ,start_index, end_index ,min_distance):
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| − | #sub array from angle to angle
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| − | s_ranges = ranges[start_index:end_index]
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| − | #filter the array
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| − | b_ranges = filter(lambda x: x <= min_distance, s_ranges)
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| − | return len(b_ranges) == 0
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| − | | |
| − |
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| − | def callback(msg):
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| − | if is_free(msg.ranges,160,200,0.2): print "FREE"
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| − | else: print "BLOCKED"
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| − |
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| − | rospy.init_node('scan_values')
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| − | | |
| − | #Put your Hamster number instead of agent<number>
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| − | #The agent number is printed on the Hamster cover
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| − | sub = rospy.Subscriber('/agent14/scan', LaserScan, callback)
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| − | | |
| − | | |
| − | rospy.spin()
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| − | | |
| − | </syntaxhighlight>
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| − | | |
| − | To execute save this example in example1.py and type in the terminal
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| − | | |
| − | <syntaxhighlight lang="bash" line='line'>
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| − | $ python example1.py
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| − | </syntaxhighlight>
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| − | | |
| − | === Python Example 2 ===
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| − | Detect right/left turn from IMU
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| − | * IMU angles are represented in Quaternions [[https://en.wikipedia.org/wiki/Quaternion]] hence translated to RPY (roll pitch yaw)
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| − | * RPY are in radians, translated to degrees
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| − | | |
| − | | |
| − | <syntaxhighlight lang="python" line='line'>
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| − | | |
| − | #!/usr/bin/env python
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| − | import rospy
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| − | import math
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| − | from sensor_msgs.msg import Imu
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| − | from tf.transformations import euler_from_quaternion, quaternion_from_euler
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| − | | |
| − | def calculate_robot_angle(orientation):
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| − | quaternion = (
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| − | orientation.x,
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| − | orientation.y,
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| − | orientation.z,
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| − | orientation.w)
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| − | euler = euler_from_quaternion(quaternion)
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| − | roll = euler[0]
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| − | pitch = euler[1]
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| − | yaw = euler[2]
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| − | return math.degrees(yaw)
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| − | | |
| − | prev_angle = 0
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| − | def callback(msg):
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| − | global prev_angle
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| − | curr_angle = calculate_robot_angle(msg.orientation)
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| − | if curr_angle > prev_angle :
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| − | print "TURINING LEFT"
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| − | else:
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| − | print "TURINIGN RIGHT"
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| − | prev_angle = curr_angle
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| − | | |
| − | | |
| − | rospy.init_node('imu_values')
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| − | last_angle = 0
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| − | | |
| − | #Put your Hamster number instead of agent<number>
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| − | #The agent number is printed on the Hamster cover
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| − | sub = rospy.Subscriber('/agent14/imu', Imu, callback)
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| − | | |
| − | | |
| − | rospy.spin()
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| − | </syntaxhighlight>
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| − | | |
| − | To execute save this example in example2.py and type in the terminal
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| − | | |
| − | <syntaxhighlight lang="bash" line='line'>
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| − | $ python example2.py
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| − | </syntaxhighlight>
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| − | | |
| − | === Python Example 3 ===
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| − | [[File:VID_20190319_171636.mp4]]
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| − | | |
| − | * The Hamster robot is a Ackermann steering system [[https://en.wikipedia.org/wiki/Ackermann_steering_geometry]] | |
| − | * This example drives the robot forward until it senses from the Lidar that there is less than a meter free ahead of it
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| − | * Motion commands should be usually published at 10Hz.
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| − | * If no motion command arrives to the robot after a second (10 messages period) the robot will stop
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| − | * Hence we send an empty message (with speed 0) to stop the robot immediately once the area is blocked ahead of it, otherwise it would stop closer to the obstacle due to the delay
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| − | | |
| − | <syntaxhighlight lang="python" line='line'>
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| − | | |
| − | #!/usr/bin/env python
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| − | import rospy
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| − | from sensor_msgs.msg import LaserScan
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| − | from ackermann_msgs.msg import AckermannDriveStamped
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| − | | |
| − | | |
| − | pub = rospy.Publisher('/agent14/ackermann_cmd',AckermannDriveStamped, queue_size=1)
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| − | | |
| − | def is_free(ranges ,start_index, end_index ,min_distance):
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| − | #sub array from angle to angle
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| − | s_ranges = ranges[start_index:end_index]
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| − | #filter the array
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| − | b_ranges = filter(lambda x: x <= min_distance, s_ranges)
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| − | return len(b_ranges) == 0
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| − | | |
| − |
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| − | def callback(msg):
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| − | global pub
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| − | if is_free(msg.ranges,160,200,1):
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| − | ack_msg = AckermannDriveStamped()
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| − | ack_msg.header.stamp = rospy.Time.now()
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| − | ack_msg.header.frame_id = 'your_frame_here'
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| − | ack_msg.drive.steering_angle = 0
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| − | ack_msg.drive.speed = 1
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| − | pub.publish(ack_msg)
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| − | else:
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| − | ack_msg = AckermannDriveStamped()
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| − | pub.publish(ack_msg)
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| − |
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| − | rospy.init_node('driving_hamster')
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| − | | |
| − | #Put your Hamster number instead of agent<number>
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| − | #The agent number is printed on the Hamster cover
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| − | sub = rospy.Subscriber('/agent14/scan', LaserScan, callback)
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| − | | |
| − | | |
| − | rospy.spin()
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| − | </syntaxhighlight>
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| − | | |
| − | To execute save this example in example3.py and type in the terminal
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| − | | |
| − | <syntaxhighlight lang="bash" line='line'>
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| − | $ python example3.py
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| − | </syntaxhighlight>
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</syntaxhighlight>
See imagery from the robot
<syntaxhighlight lang="bash" line='line'>
<syntaxhighlight lang="bash" line='line'>
sudo apt-get install ros-kinetic-desktop ros-kinetic-ackermann-*
</syntaxhighlight>
